The present invention is directed to vibration-isolation systems which are employed where there is a need to provide low cost, dependable, antivibration or vibration-isolating elements, especially where these elements must be mounted in a confined or small space and have quite low spring constants.
The invention finds particular utility in connection with vibration-isolation units which are employed to resiliently mount a chain saw engine and cutter chain assembly in a cradle-like support provided by a handle and inertia assembly.
Such composite, vibration-absorbing chain saws are featured, for example, in Frederickson et al. U.S. Pat. No. 3,542,095 (Nov. 24, 1970); Frederickson et al. U.S. Pat. No. 3,698,455 (Oct. 17, 1972); Frederickson et al. U.S. Pat. No. 3,813,776 (June 4, 1974); Bailey U.S. Pat. No. 3,845,557 (Nov. 5, 1974); and United States Bailey et al. application Ser. No. 485,424, filed July 3, 1974, entitled "Coaxial Vibrating Isolation Unit for a Chain Saw Including Discrete, Independently Operable Elements" and assigned to the assignee of the present invention.
In particular, the present invention constitutes the provision of a coaxial-type or resilient diaphragm, vibration-isolating unit uniquely suited, for example, to constitute a lowermost resilient mount interposed between a chain saw handle and the underside of a chain saw engine assembly. This invention incorporates and retains the improvements in the chain saw vibration-isolating art as disclosed and claimed in the aforesaid Frederickson et al. U.S. Pat. No. 3,542,095, and the aforesaid Frederickson et al. U.S. Pat. No. 3,813,776.
To the extent appropriate in connection with the present invention, the disclosure of the aforesaid U.S. Pat. Nos. 3,542,095; 3,698,455; 3,817,776, and 3,845,557, and the aforesaid Bailey et al. application Ser. No. 485,424 are herein incorporated by reference.
The present invention entails the use of a unique, bifurcated, resilient diaphragm structure which is characterized by a remarkably low spring rate which, in both axial and radial directions of vibration, may have a spring rate on the order of only about 50 pounds per inch.
Such an improved spring constant serves to lower the engine speeds where resonant vibration occurs, to speeds well below normal chain saw engine idling speeds and materially reduces vibrations which are transmitted through chain saw handle means to an operator during normal cutting speeds.
Indeed, with the present invention, the highest acceleration encountered over most of the chain saw cutting speed range was somewhere on the order of only about 3 G.
This reduced acceleration level is believed to be about half or less of that previously encountered with chain saw vibration-isolating systems.
This marked improvement in spring rate and acceleration characteristics of a chain saw vibration-isolating element is achieved in the context of a chain saw having a vibration-generating or vibration assembly which includes an engine having a crank shaft and a cutter chain means which traverses a cutting path about a guide bar. The chain saw further includes a support means including handle means which are to be grasped by a chain saw operator. Also included in the chainn saw are a plurality of vibration-isolating means which interconnect the vibration assembly and the support means, with at least one of the vibration means including resilient diaphragm means having an aperture extending transversely of the cutting path.
The shaft means passes through the aperture of the diaphragm means, with the diaphragm means being journaled upon the shaft means.
A first, resilient, impedance means is mounted on the shaft means and is operable to abuttingly and separably engage one side of the diaphragm means. A second, resilient, impedance means, also mounted on the shaft means is operable to abuttingly and separably engage an opposite side of the diaphragm means.
A first mounting means connects the diaphragm means with one of the vibrating assembly and support means while a second mounting means connects the shaft means with the other of the vibrating assembly and support means.
In the context of this chain saw environment, the improvement of the present invention resides in a bifurcated diaphragm means structure including a resilient, generally annular base means which is telescopingly mounted in the shaft means and located on the shaft means generally axially between the first and second impedance means. A first, resilient, generally toroidal segment means is disposed generally outwardly of and supported by the generally annular base means and is generally engageable with the first mounting means. A second, resilient, generally toroidal segment means is disposed generally outwardly of and supported by the generally annular base means and is also generally engageable with the first mounting means.
The bifurcated diaphragm means further includes a generally annular vibration and deflection-accommodating recess means which is located generally between the first and second generally toroidal segment means and encircles the generally annular base means.
The first generally toroidal segment means cooperates with the second generally toroidal segment means to define a bifurcated diaphragm means extending generally between the first and second mounting means.
Defined in a somewhat different sense, the bifurcated diaphragm means of the present invention may be considered as comprising resilient, generally annular base means telescopingly mounted on a shaft means and located on the shaft means generally axially between first and second impedance means. In this definitional aspect of the invention, a first resilient, generally annular, rim means may be considered to be spaced from the generally annular base means, as is a second resilient, generally annular rim means.
A first resilient cantilever means may be considered to be connected with the generally annular base means and resiliently support the first resilient generally annular rim means generally outwardly of the central axis of the generally annular base means. Similarly, a second resilient cantilever means may be considered as resiliently supporting the second resilient generally annular rim means generally outwardly of the central axis of the generally annular base means.
In this alternatively defined form of the invention, a generally annular, vibration and deflection-accommodating recess means is located generally between the first and second resilient generally annular rim means. The first, resilient, generally annular rim means and first, resilient, cantilever means cooperate with the second, resilient, generally annular rim means and the second, resilient cantilever means to define a generally bifurcated diaphragm means.
An independently significant facet of the invention, independent of the preferred chain saw context of the invention, and involving either of the aforegoing definitional approaches to the invention, entails the combination of the aforesaid bifurcated diaphragm means, mounted on a shaft means between first and second impedance means. This combination is believed to be applicable to vibration-isolating location and mounting arrangements other than that heretofore described and is further believed to be advantageously operable in a variety of contexts other than chain saws.
Other independently significant facets of the invention, in the context of either definitional approach, reside in features such as a generally V-shaped cross-section for the vibration and deflection-accommodating recess means, the provision of generally annular lip means on each of the first and second generally toroidal segments which are axially and radially engageable with the first mounting means, and radial clearances between the diaphragm means and either or both of the shaft means and first mounting means and axial clearances between the axial extremities of the bifurcated diaphragm means and the first mounting means.
Such independent significant is also attached to the manner in which the resilient diaphragm means, while undergoing the imposition of radially directed forces, is operable to resiliently absorb vibrations by torus bending, shear, hoop compression and axial compression and resiliently absorb vibrations while undergoing axially applied force by torus bending, shear, hoop tension and axial compresion.
A further and similarly independent, significant facet of the invention resides in a unique cushioning or "bumper" mechanism which is intended to limit or resiliently cushion radial engagement between the generally annular base means and the first mounting means. In a preferred embodiment, this cushioning or bumper structure comprises a resilient O-ring means which encircles the generally annular base means and is disposed generally axially between the first and second generally toroidal segment means (i.e., between the first and second resilient cantilever means).
In describing the invention, by way of example, but not by way of limitation, reference will be made to a preferred embodiment illustrated in the appended drawings, along with details of a modified form of the preferred embodiment provided with a cushioning or bumper mechanism.